Maria Goreti R. Vale

Current Status of Direct Solid Sampling for Electrothermal Atomic Absorption Spectrometry—A Critical Review of the Development between 1995 and 2005

Abstract The literature about direct solid sampling (SS) and slurry sampling atomic absorption spectrometry (AAS) over the past decade has been surveyed critically. It became apparent that a very significant change had occurred, particularly in the relation between the two major techniques used for that purpose. In the 1990s, slurry sampling was typically considered the technique of choice, combining the significant advantages of the solid and the liquid sampling methods, at least in part because of the availability of a commercial accessory for automatic slurry sampling. The situation is completely inverted now, as the above accessory has been discontinued and rugged and reliable accessories for direct SS became available. Direct SS electrothermal (ET) AAS has been shown to provide the best limits of detection because of the absence of any dilution and a minimal risk of contamination. Calibration against aqueous standards appears to be feasible after careful program optimization. The absence of any significant sample handling makes SS ET AAS ideally suited for fast screening analyses. The introduction of high‐resolution continuum source AAS appears to open additional attractive features for SS ET AAS because of the significantly simplified optimization of furnace programs and the visibility of the spectral environment, which makes it easy to avoid spectral interferences. New calibration strategies make a “dilution” of samples unnecessary, which used to be one of the major limitations of SS ET AAS. Finally, direct SS analysis is an important contribution to clean chemistry, as practically no reagents are used.

Atomic spectrometric methods for the determination of metals and metalloids in automotive fuels - : A review

Gasoline, diesel, ethanol and more recently also biodiesel are the four types of fuel used for automobile, truck and other transportation vehicle. The presence of metallic and metalloid species in automotive fuels is undesirable, except in the form of additives in order to improve specific characteristics of the fuel. Metallic or metalloid elements may derive from the raw product, such as nickel and vanadium in petroleum-based fuel or phosphorus in biodiesel, or they may be introduced during production and storage, such as copper, iron, nickel and zinc in case of petroleum-based fuel and alcohol or sodium and potassium in the case of biodiesel. The most famous additive to fuel is undoubtedly lead, the use of which has been banned or drastically reduced now in many countries of the world. The problems related to the trace element content may be economic, such as fuel degradation and poisoning of automotive catalysts, and/or environmental, such as the emission of metal compounds to the atmosphere. The analytical methods that have been developed for metal and metalloid quantification in automotive fuel are reviewed in this article. The main atomic spectrometric techniques used for trace metal and metalloid determination in fuels, particularly atomic absorption spectrometry with flames, graphite furnaces and with chemical vapor generation, and inductively coupled plasma coupled with optical emission and mass spectrometry are presented, including the different sample preparation procedures proposed for these techniques.

Determination of vanadium in petroleum and petroleum products using atomic spectrometric techniques

Vanadium is recognized worldwide as the most abundant metallic constituent in petroleum. It is causing undesired side effects in the refining process, and corrosion in oil-fired power plants. Consequently, it is the most widely determined metal in petroleum and its derivatives. This paper offers a critical review of analytical methods based on atomic spectrometric techniques, particularly flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ET AAS), inductively coupled plasma optical emission spectrometry (ICP OES), inductively coupled plasma mass spectrometry (ICP-MS). In addition an overview is provided of the sample pretreatment and preparation procedures for vanadium determination in petroleum and petroleum products. Also included are the most recent studies about speciation and fractionation analysis using atomic spectrometric techniques.

The use of microemulsion for determination of sodium and potassium in biodiesel by flame atomic absorption spectrometry

A new method for F AAS determination of sodium and potassium in biodiesel using water-in-oil microemulsion as sample preparation is proposed. The method was investigated for biodiesel produced from different sources, as soybean, castor and sunflower oil and animal fat and was also applied for vegetable oils. The optimized condition for microemulsion formation was 57.6% (w/w) of n-pentanol, 20% (w/w) of biodiesel or vegetable oil, 14.4% (w/w) of Triton X-100 and 8% (w/w) of water (aqueous standard of KCl or NaCl in/or diluted HNO(3)). The optimized instrumental parameters were: aspiration rate of 2 mL min(-1) and the flame composition of 0.131 of C(2)H(2)/air ratio. For comparison purpose, the determination of sodium and potassium were also carried out according to European norms (EN 14108 and EN 14109, respectively). These norms are applied for determination of sodium and potassium in fatty acid methylic ester samples and consist in the sample dilution using organic solvent and determination by F AAS. The stability of microemulsified aqueous standards and samples was investigated and it was found to be stable for at least 3 days while the organic standard diluted with xylene showed a decrease around of 15% in the analytical signal in 1h. The limits of detection were 0.1 microg g(-1) and 0.06 microg g(-1) and the obtained characteristic concentrations were 25 microg L(-1) and 28 microg L(-1) for sodium and potassium, respectively. The proposed method presented two times better limits of detection and better precision (0.4-1.0%) when compared with the dilution technique (1.5-4.5%). The accuracy of the method was evaluated through recovery tests and comparison with the results obtained by dilution technique. The recoveries ranged from 95% to 115% for biodiesel and 90% to 115% for vegetable oil samples. Comparison between the results obtained for biodiesel by both methods showed no significant differences at the 95% confidence level according to a Students t-test. This study shows that the proposed method based on microemulsion as sample preparation can be applied as an efficient alternative for sodium and potassium determination in biodiesel samples.

High-Resolution Continuum Source Atomic and Molecular Absorption Spectrometry—A Review

Abstract The present article gives an overview over the historic development, the instrumentation, the special features, and the applications of high-resolution continuum source atomic and molecular absorption spectrometry. The most obvious advantage is the need for only one single lamp for all elements and wavelengths, compared to one lamp for each analyte, as is necessary in line source atomic absorption spectrometry. The visibility of the spectral environment of the analytical line at high resolution greatly helps in method development and to avoid spectral interferences. The advanced simultaneous background correction automatically eliminates lamp flicker noise and continuous background absorption. Fine-structured background absorption may be removed using a reference spectrum and a least-squares algorithm. Because any wavelength between 190 nm and 900 nm can be accessed, the same equipment can be used for molecular absorption spectrometry, making possible the determination of non-metals, such as phosphorus, sulfur, and the halogens. Although commercial equipment for this technique has only been available for a few years, the technique has been accepted extremely well, and the number of applications that have been published using this technique has already reached an impressive number.

Slurry Sampling—An Analytical Strategy for the Determination of Metals and Metalloids by Spectroanalytical Techniques

Abstract This article critically overviews the state-of-the-art of slurry sampling as an approach for the minimization of sample preparation prior to the determination of metals and metalloids in complex matrices by spectroanalytical techniques. Relevant factors involved in the optimization of slurry-based analytical procedures and the dependence of the quality of the results on the calibration method selected are discussed in detail. The advantages and limitations compared to solid sampling for the analysis of solid matrices are highlighted and discussed. Analytical applications of slurry sampling reported in the literature emphasizing publications between 2004 and 2009 are comprehensively compiled covering detection by flame atomic absorption spectrometry (FAAS), electrothermal atomic absorption spectrometry (ET-AAS), cold vapor atomic absorption spectrometry (CV-AAS), hydride generation atomic absorption spectrometry (HG-AAS), hydride generation atomic fluorescence spectrometry (HG-AFS), inductively coupled plasma optical emission spectrometry (ICP-OES), and inductively coupled plasma mass spectrometry (ICP-MS).

Method development for the determination of manganese, cobalt and copper in green coffee comparing direct solid sampling electrothermal atomic absorption spectrometry and inductively coupled plasma optical emission spectrometry

A method has been developed for the determination of cobalt, copper and manganese in green coffee using direct solid sampling electrothermal atomic absorption spectrometry (SS-ET AAS). The motivation for the study was that only a few elements might be suitable to determine the origin of green coffee so that the multi-element techniques usually applied for this purpose might not be necessary. The three elements have been chosen as test elements as they were found to be significant in previous investigations. A number of botanical certified reference materials (CRM) and pre-analyzed samples of green coffee have been used for method validation, and inductively coupled plasma optical emission spectrometry (ICP OES) after microwave-assisted acid digestion of the samples as reference method. Calibration against aqueous standards could be used for the determination of Mn and Co by SS-ET AAS, but calibration against solid CRM was necessary for the determination of Cu. No significant difference was found between the results obtained with the proposed method and certified or independently determined values. The limits of detection for Mn, Cu and Co were 0.012, 0.006 and 0.004mugg(-1) using SS-ET AAS and 0.015, 0.13 and 0.10mugg(-1) using ICP OES. Seven samples of Brazilian green coffee have been analyzed, and there was no significant difference between the values obtained with SS-ET AAS and ICP OES for Mn and Cu. ICP OES could not be used as a reference method for Co, as essentially all values were below the limit of quantification of this technique.

Determination of cadmium, copper and lead in mineral coal using solid sampling graphite furnace atomic absorption spectrometry☆

Abstract Solid sampling graphite furnace atomic absorption spectrometry (SS-GF AAS) was investigated as a potential technique for the routine determination of trace elements in mineral coal and cadmium, copper and lead were chosen as the model elements. Cadmium and lead could be determined at their main resonance lines at 228.8 nm and 283.3 nm, respectively, but an alternate, less sensitive line had to be used for the determination of copper because of the high copper content in coal. No modifier was necessary for the determination of copper and calibration against aqueous standards provided sufficient accuracy of the results. For the determination of cadmium and lead two different modifiers were investigated, palladium and magnesium nitrates in solution, added on top of each sample aliquot before introduction into the atomizer tube, and ruthenium as a ‘permanent’ modifier. Both approaches gave comparable results, and it is believed that this is the first report about the successful use of a permanent chemical modifier in SS-GF AAS. Calibration against solid standards had to be used for the determination of cadmium and lead in order to obtain accurate values. The agreement between the values found by the proposed procedure and the certificate values for a number of coal reference materials was more than acceptable for routine purposes. The detection limits calculated for 1 mg of coal sample using the ‘zero mass response’ were 0.003 and 0.007 μg g −1 for cadmium with the permanent modifier and the modifier solution, respectively, approximately 0.04 μg g −1 for lead, and 0.014 μg g −1 for copper.

Feasibility of isotope dilution calibration for the determination of thallium in sediment using slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry

Abstract Isotope dilution (ID) calibration was investigated as a means to establish accurate values for thallium in a variety of sediment reference materials using slurry sampling electrothermal vaporization inductively coupled plasma mass spectrometry (ETV-ICP-MS) as the analytical tool. The pyrolysis curve, as well as the analysis of SRM 2704 Buffalo River Sediment, suggested that a pyrolysis temperature of 700°C could be used for this determination. The analytical results for a number of river sediment reference materials confirmed this finding; however, the results for marine sediments were far too high, indicating a serious problem with these samples. Careful investigation revealed the following interference mechanism as the most likely one. The chloride content of marine sediments is some two orders of magnitude higher than that of river sediments, and the chloride leaches out very easily into the aqueous phase of the slurry. The thallium that is in solution forms TlCl upon drying, which is easily volatilized and lost at pyrolysis temperatures >400°C. As the enriched isotope spike was added in solution, and the ‘original’ thallium is retained, at least in part, in the sediment particles, the spiked thallium is preferentially lost, leading to the excessively high analytical results. Accurate results for Tl in marine and river sediments could be obtained using pyrolysis temperatures of 400 and ≤700°C, respectively. The detection limit calculated from 3×S.D. ( n =5) of the sediment with the lowest thallium content (HISS-1) was found to be 0.003 μg g −1 . The precision at the 0.5–1.0-μg g −1 Tl level based on five consecutive readings was 1.3–4.0% R.S.D.

Simultaneous determination of Cd and Fe in grain products using direct solid sampling and high-resolution continuum source electrothermal atomic absorption spectrometry.

Cadmium and iron are antagonistic elements in the sense that they produce different effects in the human body. Both elements have to be determined routinely in grain products, cadmium because of its toxicity, and iron because all grain products, according to Brazilian law, have to contain a minimum of 42 mg kg(-1) Fe to combat anemia. A routine screening method has been developed for the quasi simultaneous determination of cadmium and iron using high-resolution continuum source electrothermal atomic absorption spectrometry and direct solid sampling. The primary absorption line at 228.802 nm has been used for Cd, and an adjacent secondary line at 228.726 nm for the determination of Fe. Various chemical modifiers have been investigated, and a mixture of tungsten and iridium, applied as a permanent modifier, showed the best performance; it stabilized Cd up to a pyrolysis temperature of 700 degrees C and did not over-stabilize Fe. Two atomization temperatures were used sequentially, 1700 degrees C for Cd and 2600 degrees C for Fe, because of their significantly different volatilities. The characteristic masses obtained were 0.9 pg for Cd and 1.2 ng for Fe. The limits of detection (3 sigma, n=10) were 0.6 microg kg(-1) for Cd and 0.5 mg kg(-1) for Fe. The relative standard deviation ranged from 3 to 7% for Cd and from 4 to 13% for Fe, which is satisfactory for the purpose. The accuracy of the method was confirmed by the analysis of three certified reference materials; the results were in agreement with the certified values at a 95% confidence interval. The Cd content in the investigated grain products was between 0.9 and 10.5 microg kg(-1), but most of them did not contain the required minimum amount of iron.